是否可以使用变量按名称引用字段？

var person = {
  name: 'John',
  age: 30,
  gender: 'male'
};

var fieldName = 'age';
console.log(person[fieldName]); // 输出：30

import java.lang.reflect.Field;

public class Main {
  public static void main(String[] args) throws Exception {
    Person person = new Person("John", 30, "male");

    String fieldName = "age";
    Field field = person.getClass().getDeclaredField(fieldName);
    field.setAccessible(true); // 如果字段是私有的，需要设置可访问性
    Object fieldValue = field.get(person);

    System.out.println(fieldValue); // 输出：30
  }
}

class Person {
  private String name;
  private int age;
  private String gender;

  public Person(String name, int age, String gender) {
    this.name = name;
    this.age = age;
    this.gender = gender;
  }
}